Band spread arrangement in superheterodyne receivers



Aug. 6, 1940. D, PA'S A 2 .210.379

BAND SPREAD ARRANGEMENT IN SUPERHETERODYNE RECEIVERS Filed Dec. 16, 1938 2 Sheets-Sheet l INVENTOR DOUWE PASMA BY A l'TbRNEY Aug. 6, 1940.

D. PASMA 2.210379 BAND SPREAD ARRANGEMENT IN SUPERHETERODYNE RECEIVERS Filed Dec. 16, 1938 2 Shets-Sheet 2 KY9: E7,

FREQUENCY RANGE 11701.9 M. 6 EAN0-$PREA0 Ar a-14M. b-UM. 69 v ilk ' 4| j FREQUENCY RANGE 18 To M.

EAN0-$RREA0 Ara-19M. 17-25114. 67 69 73 3 Ya #l 11 I a I .42 b

A FREQUENCY RANGE 29 70 .54 M 6 EAN0sPREAo Ar a-31M. b-49M. -72 15 6.9 .4 AP

3nventoz mm Ba/Jmw, y

attorney Patented Aug. 6, 1940 FATE 1' arts BAND SPREAD ARRANGEMENT IN SUPER- HETERODYNE RECEIVERS Douwe Pasma, Eindhoven, Netherlands, assignor, by mesne assignments, to Radio Corporation of America, New York, Delaware N. Y., a corporation of Application December 16, 1938, Serial No. 246,093 In the Netherlands May 11, 1938 11 Claims.

This invention relates to a superheterodyne Wireless receiving set capable of being tuned to a number of comparatively wide frequency-bands and, particularly for high-frequencies, to a numher of comparatively narrow frequency-bands comprised within one or more of the said frequency-bands.

In a set capable of being tuned to a number of broadcasting wave bands and to one or more short-wave bands, for tuning use is generally made of the variable condensers which serve for tuning to the first-mentioned wave-bands. This permits of the entire short-wave spectrum being divided in only a few wave-bands overlap- 15 ping one another. This has, however, the following disadvantage.

The wave-lengths of the short-wave transmitters being united in a number of comparatively narrow frequency-bands, tuning is difficult, since the wave-lengths of the transmitters, comprised in the same band, are immediately adjacent each other on the tuning dial.

It is well known to meet this diificulty by utilising so-called band-spread.

Forobtaining band-spread it has already been proposed to connect in parallel with each of the circuits a small variable condenser by means of which the oscillatory circuit concerned can be tuned within a narrow frequency-band. This solution leads, however, to a highly complicated and costly circuit arrangement.

According to the invention, a substantially simplified circuit arrangement is obtained in that, on passing from at least one of the comparatively wide frequency-bands to at least one of the comparatively narrow frequency-bands comprised therein, the variable tuning members of the oscillatory circuits which precede the first detector are locked by hand or automatically in a position in which the circuits are tuned approximately to the middle of the comparatively narrow frequency-band concerned, whereas during reception of the comparatively narrow frequencybands only the oscillatory circuit of the oscillator is tuned.

According to a further feature of the invention, on passing from at least one of the comparatively wide frequency-bands to at least one of the comparatively narrow frequency-bands comprised therein, the variable oscillator condenser used for one or more comparatively wide frequency-bands is replaced by hand or automatically by the parallel combination of a fixed condenser and a variable condenser, small as compared with the said oscillator condenser.

In this case it is also frequently preferable that an inductance and/or a trimmer condenser corresponding to that comparatively narrow band should be connected in parallel with the oscillator circuit.

The inductance coil which is connected in parallel with the oscillatory circuit preferably forms part of the oscillatory circuit when a neighboring comparatively wide frequency-band is received. The division of the wave-bands is preferably such that each of at least two of the comparatively wide frequency-bands comprises two or more of the comparatively narrow frequency-bands and that there is at least one position of the tuning members at which the receiver is tuned, in each of the said wide frequencybands, to a frequency which is intermediate two of the said narrow frequencybands.

According to a suitable form of the invention each of the comparatively narrow frequencybands comprised within a comparatively wide frequency-band is associated with a trimmer condenser to which respectively the connections are automatically changed when the tuning members move through one of the said positions.

In order that the invention may be clearly understood and readily carried into efiect one embodiment thereof will now be described more fully with reference to the accompanying drawings, wherein Fig. 1 illustrates the oscillator portion of a superheterodyne circuit according to the invention. Fig. 2 discloses the mechanical arrangement that may be utilized for operating the band-spread means of Fig. l, and Figs. 3, i and 5 are the circuits obtained with adjustments of the wave-band switch to the highest frequency range (11 to 19 m.) to the next lower frequency range (18 to 30 m.), and to the second next lower frequency range (29 to 54 m.), respectively.

Referring to Fig. l; I, 2, 3, i, 5 and 5 designate six induction coils serving for a number of shortwave, intermediate wave and long-Wave bands. These induction coils have one of their ends earthed and their other ends connected respectively to the contacts, H, 52, is, M, i5 and [6 of the section Iii of the wave-band switch. This section [B comprises a movable conductor 11 which can be connected in succession to the contacts ll, [2, i3, Hi, l5 and it by means of a contact 18. A contact is which is continuously connected to the conductor 5'! is connected to the switch-lever 33 of a switch 2 3. The induction coils 2, 3, i and 5 are provided with tappings which are connected respectively to the contacts Q2, 43, 44 and 45 of the section 40 of the waveband switch. The coils I and 6 have coupled to them coils I and 8, earthed on one side, whose ends, not earthed are connected to the contacts ll and 46 of the section 46. The section it comprises a movable conductor 41 which can be connected in succession to the contacts M, M, 13, 44, 45 and 46 by means of a contact 58. A contact 49 which iscontinuously connected to the conductor 41 is connected to the cathode 51- of an oscillator valve 60.

The section of the wave-band switch comprises a movable conductor 21 which can be connected in succession to the contacts 2! and 3E, 22 and 32, and 23 by means of contacts 28 and 38. A contact 29 which is continuously connected to the conductor 21 is connected to the contact 26 of the switch 24. A large variable condenser 34 is connected between the contact of the switch 24 and earth. A fixed condenser 35 and a small variable condenser 36 are connected between the con-tact 26 of the switch 2 3 and earth. An inductance" 9 is connected between the contact Z! of the section 20 of the wave-band switch and earth. The contact 22 is connected to the contact H of the section ill. The contacts 35, C52 and 23 of the section 2b are connected respectively to the switch-levers 5!, 52 and 53 of the switch 50. The switch 5!) has two positions, viz. an a-position and a la -position respectively, inwhich the levers El, 52 and 53 contact respectively with the contacts 5m, 52a, 53a and Bib 52h, 53h respectively. Trimmer condensers 5d, 55 56:, 5 58 and. 59. are connectedrespectively between the contacts 51a, 55b, 52a, 52b, 53a, 53b, and earth. In the third switch-position of the wave-band switch the coil .3 is included in the oscillator circuit. In this position of the waveband switch the two contacts 37 and 39 of a switch 33 are bridged by the contact 39, which may be efiected, for example, by causing the switch 39' to form part of a section of the waveb'and switch. The contact 31 of the switch 30 is connected to the contact 53a. The contact 39 of the switch 30 is connected to the contact E2 of the section In of the wave-length switch. The switches 24 and 50 are coupled mechanically to the variable condenser 34, as is indicated by dotted lines 84, 65', 56. The switch 5B occupies the w-position for part of the angle of rotation of the" condenser 34 and occupies the b-position for the remaining part. The switch lever 33 of the switch 24 contacts with the contact 25 for reception of the comparativelywide fre quency bands and is connected to the contact 26 in a manner hereinafter described on passing to reception of the comparatively narrow frequency bands. The control grid 62 of the oscillator valve 6!! is connected to the switch lever 33 of the switch 24 by the intermediary of a condenser B1 and to earth by the intermediary of a resistance 68'. The anode 63- is connected to a positive voltage relatively to earth and is connectedto earth via a condenserfifl. The cathode BI is at a highfrequency voltage which it can feed via a condenser lll, to a conductor H", earthed via a resistance 12. During reception of the comparatively wide frequency bands the oscillatory circuit comprises the rotary condenser 34 and one of the inductance coils I, 2, 3, i, 5 or 6. The coils l, 2, 3 and d are short-wave coils and serve respectively for reception of the following frequency-bands: 11 m. to 19 m., 18 m. to 30 m., 29 m. to 54 m., 52 m. to 1'77 m. The coils 5 and 6' serve respectively for reception of the intermediate-wave range 1'72 m. to 570 m. and the long-wave range 7&0 m. to 2100 m.

In the first wave-range use is made of bandspread at 14 m. and 1'? m., in the second waverange at 19 m. and at 25 m. and in the third wave-range at 31 and at 49 m. The section it? of the wave-switch serves for changingthe connections of the ends of the inductance coils i, 2, 3, 5, 5 or 6. The section 40 which is connected to, the cathode of the oscillator valve connects this cathode for the coils 2, 3, 4, 5 to a tapping on the coil, for the long-wave coil 6 to the end, not earthed, of the coil 8, coupled to the coil 6, and for the coil 5 to the end, not earthed, of the coil '5, coupled to the coil l. The oscillator acts on the second, third, fourth and fifth Waverange accnrding to the three-point Hartley circuit arrangement. The feedback coupling to the first sixth wave-range is effected in purely inductive manner. The control grid 62 of the oscillator valve til is connected so far as high frequencies are concerned in succession to the ends, not earthed, of the oscillatory circuits. The anode 65' is earthed so far as high frequencies are concerned, whereas the cathode is at a high-frequency potential. For stable oscillation the inductive feedback coupling is necessary for the lowest and highest frequencies As mentioned before, each of the three short-' wave bands comprises two narrow frequencybands for which band-spread can be utilised. In order to permit of receiving with band-spread the high-frequency oscillatory circuit and the local oscillator circuit are tuned to the middle of the desired narrow frequency-band. The obtainment of correct tuning is made known by a clicking sound or by a binding of the tuning members as will be explained hereinafter in connection with 2; At thismoment the oscillatory circuits preceding the first detector are left as they are. The variable condenser 34 of the local oscillator circuit is automatically cut out by the switch 24 being moved. It is replaced by the parallelcombination of a fixed condenser 35 and a small variable condenser 36. As shown by Fig. 3 which represents the condition of the circuit in the first positioned the wave-band switch, the two last-mentioned condensers (35 and 36) have the coil aconnected in parallel with them, by the intermediary of the section 2t and the contacts 29, 28 and 38, and in the position shown of the switch 5 5, the trimmer condenser 54. The oscillatory circuit is thus constituted by the parallel-combination of the coils I and 9 and the condensers 35, 365 and either 54 or 55, in accordance with the position of the switch arm 55 of the switch 58, which; as already mentioned, depends on the position of the tuning condensers and consequently of the narrow frequency-bands to which tuning has been effected.

As shown by Fig. 4 which represents the condition of the circuit in the second position of the wave-band switch, in the case of band-spread reception, the coil 5 and the trimmer condensers .56 or 51 are connected in parallel with the con.- densers i5 and 35. The oscillatory circuit in this position of the wave-band switch is thus constituted by the parallel-combination of the coil 2 and the coil l (which is utilized in the highest frequency-band) the parallel-combination of the fixed and variable condensers 35 and 35, respectively, and either condenser 5 5 or 51, depending upon the positions of the switch arm 52 of the switch 58.

As shown by Fig. 5 which represents the condi- 75 tion of the circuit in the third position of the wave-band switch, in the case of band-spread reception, the trimmer condensers 53 or 59 are connected in parallel with the condensers 35 and 36. When the switch arm 53 of the switch 56 oocupies the a-position, the coil 2 (utilized in the next higher band) is also connected in parallel with the condensers 3E, 36 and 58 through the switch 30 which is closed in the third position of the wave-band switch. In the b position of the switch arms 53 the coil 2 is cut out.

The trimmer condensers 55, 58, 51', 58 and 59 permit the oscillatory circuit to be adjusted for reception of the narrow frequency-bands. On passing to band-spread reception, the inductances in the oscillatory circuit are preferably reduced in order to permit the capacities to be increased, since this is desirable for permitting the relative capacity variation, which occurs due to the rotation of the condenser to be maintained small.

In order to receive the 49 meter-band with the same absolute band-width as the 31 meter-band it is necessary for the relative capacity variation to be larger than with the last-mentioned band so that the fixed capacity, connected in parallel with the oscillatory circuit, should be smaller.

When receiving the 49 meter-band no inductance is therefore needed to be connected in parallel with the inductance, already present in the oscillatory circuit.

In this example, on passing to band-spread reception the inductances are reduced by connecting in parallel with the coil. in operation a coil of lower inductance i. e. the coil of the neighboring wave-range. Only for the 14 meter and 1'7 meter bands is there a separate coil which is'connected in parallel with the coil I. Further more, the coil I is connected in parallel with the coil 2 for the 19 meterand 25 meter-hands and the coil 2 is connected in parallel with the coil 3 for the 31 meter-band. When passing to the 49 meter-band the coil 2 is cut out by the switchlever 53 of the switch 58.

When the tuning condenser is rotated further the switch 24 is directly connected back to occupy the former position on contact 25 so that the set is again ready for reception without band-spread.

The mechanical coupling ss ee between the shaft of. the tuning condenser 34 and the switch 50 is constituted by a stop on the edge of a disc fixed to the condenser shaft, said disc moving in a given position the switch till.

The mechanical coupling i i-555 between the shaft of the tuning condenser and the switch 24 is shown in Fig. 2 and comprises three discs arranged on the condenser shaft 5% of which only one (IIBI) is shown in the figure and each of. which serves for one of the comparatively wide frequency-bands to which band-spread is applied. Each of these discs has two notches I84, I95 formed in it at points which are determined by the disposition of the comparatively narrow frequency-bands within the comparatively wide frequency-bands. disc has arranged opposite it a spring which is adapted to rotate in the middle about a shaft H3. One of these springs is shown in the figure and designated by Ilil. In unstressed condition. this spring III! engages with its head IM the disc lill and with its tail H5 the roller Ill which is fast on the shaft N5 of the wave-band switch and which is provided with studs I I8, H9 and HM. When the roller Ill rotates, the studs H8, H9

and I20 move in parallel planes containing the centre lines of the three springs, arranged in succession. Each stud can apply to one of the springs a bias tension which enables this spring to snap into a notch. Each of the heads of the springs is connected to a lever adapted to rotate about a shaft WI. The three levers have their lower ends bearing on a stop I25 of a rod I26 of insulating material. In Fig. 2 one of the levers is designated by I22. The rod IE6 is supported by guides I28 and I25 and forced by a spring I21 against the ends of the levers. The rod I26 is provided with two contacts I30 and [BI which contact alternately with a rod I32.

When reception occurs in a frequency-band in which band-spread is possible, one of the springs has a bias tension. As soon as, during rotation of. the condenser-shaft I00, a notch arrives in front of the head of this spring, the latter snaps into it and pulls down the associated lever so that the contact I3II32 is closed. The contacts Isl] and ISi correspond to the contacts 25 and in; of the switch 24 of Fig. 1. The set is thus in readiness for band-spread reception. When rotation of the condenser shaft IE0 is continued the previous condition is reestablished.

The rod 52% may be provided with a few more supplementary contacts in order to short-circuit the condensers not used, for the purpose of avoiding losses.

I claim:

1. A superheterodyne wireless receiving set capable of being tuned to a number of comparatively wide frequency-bands and, particularly for high-frequencies, to a number of comparatively narrow frequency-bands comprised within one or more of the said wide frequency-bands, comprising a high frequency portion and a local oscillater, variable tuning means in the high frequency portion common to all the frequencybands, variable tuning means in the local oscillator circuit which is also common to all the frequency-bands, means cooperating with said variable tuning means whereby, on passing from at least one of the comparatively wide frequencybands to at least one of the comparatively narrow frequency-bands comprised therein, the variable tuning means of. the high frequency oscillatory circuits which precede the first detector are locked in a position in which the circuits are tuned approximately to the middle of the comparatively narrow frequency-band concerned, and means actuated by said locking means for disconnecting the variable tuning means of the local oscillator and substituting therefor the parallel combination of a fixed condenser and a variable condenser, the latter being small. as compared to the disconnected tuning means.

2. A superheterodyne wireless receiving set as claimed in claim 1, wherein on passing from at least one of. the comparatively wide frequencybands to at least one of the comparatively narrow frequency bands comprised therein a trimmer condenser corresponding to the said comparatively narrow band is connected in parallel with the substituted parallel combination of the fixed and variable condensers.

3. A superheterodyne wireless receiving set as claimed in claim 1, wherein on passing from at least one of the comparatively wide frequencybands to at least one of the comparatively narrow frequency-bands comprised therein an inductance is connected in parallel with the substituted parallel combination of the fixed and variable condensers.

4. A superheterodyne wireless receiving set as claimed in claim 1, wherein on passing from the highest frequency-band to the next highest band, the inductance of the tuned circuit utilized in the former band is connected in parallel with the substituted parallel combination of fixed and variable condensers.

5. A superheterodyne wireless receiving set as claimed in claim I, wherein the condenser shaft for. each comparatively wide frequency-band to which bandspread is applied has fast on it a disc which has formed in it as many notches as there are comparatively narrow frequency-bands in the comparatively wide frequency-band concerned, at points which register with the disposition of the narrow frequency-bands, each disc being. associated with a spring which, after being selected, is adapted to snap into the said notches and which brings about the change of connections for band-spread reception.

6. In a multiband receiving circuit of the superheterodyne type, an electron discharge tube, a plurality of inductances, one for each frequency band, wave-change mechanism for selectively connecting one of said inductances in a circuit associated with said tube, a variable tuning condenser normally connected in shunt to each of. said selected inductances to form a tuned circuit therewith responsive to the selective frequency band, auxiliary tuning means, and means under the control of said tuning condenser and operative only in the reception of certain of the frequency bands for disconnecting said tuning condenser after rotation thereof, through a predetermined angle and substituting therefor the auxiliary tuning means.

7. The combination defined in claim 6, wherein the auxiliary tuning means comprises the parallel combination of a fixed condenser and a variable condenser.

8. In a multi-band receiving circuit of the superheterodyne type, a local oscillator circuit including an electron discharge tube, a plurality of inductances, one for each frequency band, wave-change mechanism for selectively connecting one of said inductances in the local oscillator circuit, a variable tuning condenser normally connected in shunt to each of said selected inductances to form a tuned circuit therewith, auxiliary tuning means, and means under the control of said tuning condenser and operative only in the reception of certain of the frequency bands for disconnecting said tuning condenser after rotation thereof through a predetermined angle and substituting therefor the auxiliary tuning means.

9. The combination defined in claim 8 wherein with the adjustment of the wave-change mechanism for the highest frequency band an auxiliary inductance is shunted across the substituted auxiliary tuning means.

10. The combination defined in claim 8 wherein with the adjustment of. the wave-change mechanism for the highest frequency band an auxiliary inductance is shunted across the substituted v20 auxiliary tuning means, and with adjustments of only in the reception of certain of the frequency 7 bands for disconnecting said tuning condenser after rotation thereof through a predetermined angle and substituting therefor the auxiliary tuning means, and means under the control of said wave-change mechanism for introducing an additional inductance; in shunt to the auxiliary tuning means, at least for adjustments of. the Wave-change mechanism for the highest frequency bands. Y I

DOUWE PASMA. 

